Nestled near the start of Harry Potter and the Prisoner of Azkaban is a blink-and-you'll miss it cameo from former Stone Roses frontman Ian Brown. But the erstwhile King Monkey is not the first to enjoy 15 seconds of fame in an otherwise unrelated movie. Other classic cameo players include Nelson Mandela, Marshall McLuhan and Leon Trotsky ... allegedly.

Nelson Mandela in Malcolm X (1992)

Nelson Mandela's movie career was a brief one indeed: shoe-horned into that period just after his release from prison and just before he became president of South Africa, won the Nobel peace prize and met the Spice Girls. In effect it boils down to a winsome appearance in Spike Lee's biopic of American black nationalist leader Malcolm X. Mandela plays a Soweto schoolteacher addressing his pupils who one by one declare, "I am Malcolm X." Coming at the very end of the film, Nelson's appearance was doubtless intended to add a touch of poignancy and gravitas to an already powerful and furious evocation of one of the most fractured episodes in modern America's history. So we shan't mention any likeness to Coke ads and the climax to Spartacus.

Leon Trotsky in My Official Wife (1914)

When he wasn't fomenting Russian revolutions, Lev Davidovich Bronstein - Leon Trotsky to you and me - appears to have enjoyed a brief sideline as a movie extra. The goateed icon seems to crop up as one of a crowd of nihilists in this 1914 espionage pot-boiler. He reputedly even provided the studio with a stage name, Mr Brown, for payment purposes.

Annoyingly, though, there are some who dismiss Trotsky's film career as a fiction. According to silent cinema historian Kevin Brownlow, Trotsky did indeed spend time exiled in New York editing Russian language journal Novy Mir (New World) - but that was two years after this film was made. The extra in an oft-produced still who is the spitting image of the future revolutionary and ice-pick caddy is, he says, merely that. Print the legend, we say.

George Harrison in The Rutles: All You Need is Cash (1978)

He didn't write the Frog's Chorus. He never had a televised lie-in. He didn't once show up in a Jacky Collins' TV mini-series. It didn't take much for George Harrison to keep his cool longest once the Beatles had called it a day. But popping up as an interviewer in a film which so comprehensively (if affectionately) spoofed the whole Beatlemania myth was surely the coolest post-Fabs act of all. Although Ringo did push him close by playing the Pope in Ken Russell's camp-out, Lisztomania.

Harpo Marx as in The Story of Mankind (1957)

At the height of the Marx brothers' success in the 1930s, Harpo - the mute, grinning one - invariably played mute, grinning characters with names like Pinky, Punchy, Wacky and, er, Harpo. So, when conceiving this condensed history of the world, it's obvious what was going through director Irwin Allen's mind: what could possibly be funnier than Isaac Newton discovering gravity not by a single apple falling on his head but, wait for it, an entire harvest of them? Someone should have told him.

Marx goes through his bit-part on auto-pilot, as if embarrassed by the whole charade. It was his last role of any sort before his death seven years later. Meanwhile Allen - a sort Ed Wood with bigger budgets - went on to make bank holiday fodder like Voyage to the Bottom of the Sea, The Swarm and The Poseidon Adventure.

Sean Connery in Robin Hood: Prince of Thieves (1991)

The classic film cameo relies on an 'ooh' factor. Think of it as a hidden treat, intended to distract the audience's attention ever so briefly, preferably with a knowing wink. But Sean Connery's 30-second pop-up as King Richard was just too potent for comfort, particularly coming after the pallid heroics of Kevin Costner's Hood. Stories abound of cinema audiences responding less with a chorus of 'oohs' than with rapturous standing ovations. Anyone would think it were the highlight of the movie. Which funnily enough...

Marshall McLuhan in Annie Hall (1977)

As a general rule of thumb, noted academics tend to avoid movie cameos (surely it's not because Hollywood isn't asking them). So the undisputed don of a select band remains communications theorist Marshall McLuhan ("the medium is the message", "all advertising advertises advertising"... they were his) who makes the most of his 15-seconds of stardom in Woody Allen's Annie Hall. While queuing for cinema tickets, Alvy Singer (Allen) takes issue with a fellow moviegoer's monologue on the merits of McLuhan's writings on communications and modern media. As the pair start to argue, Alvy pulls a masterstroke and drags McLuhan out from behind a hoarding to tell the other guy, "you know nothing of my work!"

Alfred Hitchcock in Lifeboat (1944)

Spotting Hitch in his movies is cinema's version of Where's Wally. He's always there. On the bus in To Catch a Thief, or missing the bus completely at the start of North by Northwest. Passing by on the street or hanging out in a crowd of onlookers. But the porcine director's most cunning cameo came in Lifeboat, ingeniously navigating a seemingly impossible hurdle (one small boat, eight shipwreck survivors) by playing the "before and after" photos in a newspaper advertisement for dieting aid, Reduco Obesity Slayer. This proved particularly fitting, since Hitchcock lost 100 pounds during the film's production.